Controlled radial magnetic bearing

ABSTRACT

The flux densities formed by plural electromagnet poles M 1  to M 12  which are arranged at a predetermined interval in a circumferential direction of a rotary body  1  at the same position in an axial direction of the rotary body  1  are gradually changed in the circumferential direction of the rotary body. Even if there is a difference between the maximum value of the flux density and the minimum value, the change of the flux densities between the adjacent electromagnet poles is small and smooth. Accordingly satisfactory detective sensitivity and detection results can be obtained.

TECHNICAL FIELD TO WHICH THE INVENTION RELATES

This invention relates to a controlled type magnetic radial bearingwhich supports a rotary body used for an energy-storage flywheel, anultra high-speed rotating body or the like in a non-contact manner in aradial direction.

BACKGROUND ART

Controlled type magnetic bearing devices, which magnetically levitate arotary body for supporting in a non-contact state, have been widely usedin various fields in recent years since the loss accompanied by rotationcan be remarkably reduced.

Generally a controlled type magnetic bearing device is provided with agroup of controlled type magnetic axial bearings which support a rotarybody in a non-contact state in an axial direction and two groups ofcontrolled type magnetic radial bearings which support the rotary bodyin a non-contact state in a radial direction. The magnetic radialbearing is equipped with plural electromagnets (usually four pieces)which are arranged at equal intervals in a circumferential direction ofthe rotary body. Each of the electromagnets is provided with a magneticpole having a salient pole, which projects inside in a radial directionand opposes an outer periphery of the rotary body, and a coil forfeeding an exciting electric current is wound around the magnetic pole.The exciting current is combined with a constant bias current and acontrol current controlled dependent on the displacement of the rotarybody. A magnetic flux combined with a constant bias magnetic flux by thebias current and a control magnetic flux by the control current isformed in each of the magnetic poles.

In such a controlled type magnetic radial bearing, there is a problemcaused by eddy current loss produced inside a rotary body at ahigh-speed rotation. An eddy current is generated when a flux densityvaries in a circumferential direction of the rotary body and themagnitude of the eddy current is proportional to the variation of fluxdensity.

There are hetero-polar type and homo-polar type magnetic radial bearingsaccording to the structure of an electromagnet. In the hetero-polar typemagnetic radial bearing, each of the electromagnets has magnetic polesat two positions in a circumferential direction of the rotary body andthe two magnetic poles are excited in opposite polarities by supplyingan exciting current to coils. Since a plurality of such electromagnetsare arranged in the circumferential direction of the rotary body, themagnetic poles with reversed polarities are arranged adjacently to eachother in the circumferential direction of the rotary body. Therefore,the flux density around the rotary body is largely varied along thecircumferential direction of the rotary body, a large eddy current flowsinside the rotary body to generate an eddy current loss and increase therotation loss.

On the other hand, in the homo-polar type magnetic radial bearing, eachof the electromagnets has magnetic poles in two positions in the axialdirection of a rotary body and two magnetic poles are excited withreversed polarities by supplying an exciting current to coils. Bysupplying the exciting currents so that the magnetic poles on the sameside in the axial direction of the rotary body may become the samepolarity, only the magnetic poles with the same polarity are arranged onthe same side in the circumferential direction of the rotary body.Therefore, the change of the flux density becomes small along thecircumferential direction of the rotary body. However, since there isstill a difference of flux density between a portion with a magneticpole and a portion with no magnetic pole, the change of flux density isgenerated between the magnetic poles arranged adjacently to each otherin the circumferential direction of the rotary body. Therefore,approximately half the eddy current in the case of the hetero-polar typedescribed above flows to generate approximately half the rotation lossof the hetero-polar type.

The eddy current described above can be decreased to a level havingsubstantially no problem for an ordinary device by using laminated steelplates for the rotor part of a rotary body opposing the electromagnet.However, there have been increasing applications in recent years inwhich the loss of eddy current and the rotation loss due to the eddycurrent practically cause problems even though laminated steel platesare used for the rotor part of a rotary body in a device such as anenergy-storage flywheel and an ultra high-speed rotary body.

Therefore, it is an object of the present invention to provide acontrolled type magnetic radial bearing which is capable of suppressinggeneration of an eddy current to reduce the rotation loss in order tosolve the above-mentioned problem.

DISCLOSURE OF THE INVENTION

According to the present invention, the above-mentioned object isachieved by a controlled type magnetic radial bearing provided withplural electromagnet poles which are arranged at a predeterminedinterval in a circumferential direction of a rotary body at the sameposition in an axial direction of the rotary body and all of theelectromagnet poles are set to be the same polarity, characterized inthat the flux densities formed by the electromagnet poles are graduallychanged in the circumferential direction of the rotary body. The changeof the flux densities in the circumferential direction of the rotarybody becomes small and smooth. As a result, the eddy current generatedin the rotary body during rotation is decreased, an eddy current lossand rotation loss are reduced and extremely satisfactory rotationalcharacteristics can be obtained with a simple constitution at low cost.

Here, “the flux densities are gradually changed” means that even ifthere is a difference between the maximum value of the flux density andthe minimum value, the change of the flux densities between the adjacentelectromagnet poles is small and smooth.

Generally, plural electromagnet poles are arranged at equal intervals inthe circumferential direction of the rotary body.

The present invention can be applied to any of conventional homo-polartype magnetic radial bearings in which an electromagnet forms a magneticfield only by a coil and conventional hybrid type magnetic radialbearings in which a permanent magnet forms a bias magnetic flux and anelectromagnet forms a control magnetic flux by a coil. Moreover, thepresent invention can be applied to magnetic axial and radial bearings,which support both in the axial and radial directions in a non-contactstate. In any case, the electromagnet is equipped with magnetic poleswith a coil. The magnetic pole may have a salient pole or may bedirectly fitted with a coil on the inner peripheral face of acylindrical stator without a salient pole. Moreover, the magnetic polecan be formed in a so-called closed slot type in which both of the tipend faces of adjacent salient poles are connected with each other by athin protruded part.

The flux densities of the respective electromagnet poles become themaximum on the side where the rotary body is magnetically attracted andbecome the minimum on the opposite side. The change of the flux densityis set to be, for example, in a shape of a cosine wave (or a shape of asine wave) so as to change the flux density gradually between them.

In the case of hybrid type magnetic radial bearings in which anelectromagnet has a permanent magnet, the polarity in the total magneticflux combined with the bias magnetic flux by the permanent magnet andthe control magnetic flux by a coil is set to be the same polarity withrespect to all the electromagnets.

Therefore, according to the controlled type magnetic radial bearing ofthe present invention, since the flux density of the electromagnet poleschanges continuously and gradually in a circumferential direction of therotary body, the change of the flux density in a circumferentialdirection of the rotary body becomes small and smooth and the eddycurrent generated in the rotary body during rotation is reduced to makean eddy current loss and its rotation loss become small.

Also, in a controlled type magnetic radial bearing of the presentinvention, for example, at least three electromagnet poles are providedand the flux density by each of the electromagnet poles is variedgradually and continuously in the circumferential direction of therotary body. The change of the flux density in the circumferentialdirection of the rotary body becomes small as a whole by means of thatthe flux densities of the respective electromagnet poles are graduallychanged, and the eddy current is reduced to decrease the eddy currentloss and rotation loss.

The change of the flux densities in the circumferential direction of therotary body can be made smaller as the number of the electromagnet polesis increased and the number of the electromagnet poles is desirable tobe the multiple of 4 or 3. In these cases, the control current can becontrolled like the conventional controlled type magnetic radialbearings which have four electromagnet poles in the circumferentialdirection and the control current can be controlled easily. Therefore,the number of the electromagnet poles is preferably eight or more. Inthe case of the multiple of 3, it can be controlled by using athree-phase inverter widely used for driving a motor.

Furthermore, in the controlled type magnetic radial bearing according tothe present invention, the flux densities by respective electromagnetpoles can be gradually changed in the circumferential direction of therotary body by, for example, adjusting the control current supplied tothe coil of respective electromagnet poles. By adjusting the controlcurrent supplied to the coil of respective electromagnet poles, thechange of the flux densities of respective electromagnet poles becomessmall and the eddy current is reduced to decrease the eddy current lossand rotation loss.

At this time, the control current in respective electromagnet polesbecomes, for example, the maximum value in the positive direction(“positive direction” is the direction of the control current whichgenerates control magnetic flux as the same direction as the biasmagnetic flux) on the side where the rotary body is attracted. Thecontrol current becomes the minimum value in the negative direction(“negative direction” is the direction of the control current whichgenerates control magnetic flux as the opposite direction to the biasmagnetic flux) on the opposite side. Further, the change of the controlcurrent between them is set so as to be in a cosine wave shape. As aresult of that, the flux densities of respective electromagnet polesbecome the maximum on the side where the rotary body is attracted andbecome the minimum on the opposite side and, moreover, the change of theflux density between these maximum and minimum forms in a cosine waveshape.

For example, when the number of the electromagnet poles is a multiple of4, two electromagnets are arranged in each of two control axes of theradial direction which are perpendicular to each other as a conventionalcontrolled type magnetic radial bearing having four electromagnets.These four electromagnets are main electromagnets. In this case, thenumber of turns of the coil in each electromagnet pole is set to be anumber of turns proportional to a sine wave or a cosine wave.

That is, when there are provided eight magnetic poles, the numbers ofturns of the coils in the case of controlling in the up and downdirection are set to be winding ratio of“1:0.707:0:−0.707:−1:−0.707:0:0.707” from the upper magnetic pole(negative means winding in the opposite direction) and the coils areconnected in series. Here, 0.707=cos 45°. This value is the number ofturns of the coil for making a magnetic field into a form similar to acosine wave. In this example, displacement signals of the up and downdirections are detected, and an operational signal for controlling at aregular position is generated and applied to the coil.

On the other hand, in the case of a hybrid type magnetic radial bearing,the coils of two electromagnet poles at a position opposing each otherin the radial direction are connected in series and the same controlcurrent is fed in the two coils. Further, the winding directions of thetwo coils are set to be opposite in such a manner that, when the samecontrol current is supplied to the coils of the two electromagnet polesopposing each other, the magnetic fluxes formed by the coils becomeopposite polarities to each other. That is, when the same controlcurrent is fed in the coils of the two electromagnet poles opposing eachother, one is set in the positive direction and the other is set in thenegative direction. Therefore, the number of amplifiers can be reducedto half the number of electromagnet poles.

Also in this case, by supplying the same reference control current tothe coils of the magnetic poles of two main electromagnets with respectto each control axis, the reference control current in the positivedirection is fed to the coil of the magnetic pole of one of the mainelectromagnets and the reference control current in the negativedirection is fed to the coil of the magnetic pole of the other of themain electromagnets. Control currents, which are changed in a cosinewave shape when the reference control current in the positive directionis regarded as “1”, are supplied to the sub-electromagnets. In this way,the control currents in each of the electromagnet poles become themaximum value in the positive direction on the side where the rotarybody is attracted and the minimum value in the negative direction on theopposite side and, moreover, the control current is changed in a cosinewave shape along the whole circumferential direction of the rotary body.Consequently, the total flux density combined with the bias magneticflux by the permanent magnet and the control magnetic flux by thecontrol current becomes the maximum value on the side attracting therotary body and the minimum value on the opposite side, and the changeof the flux density along the whole circumferential direction of therotary body becomes a cosine-shape.

In addition, in a controlled type magnetic radial bearing according tothe present invention, for example, plural groups of coils to which thecontrol current is individually supplied are provided, the coils ofrespective groups are wound around predetermined plural electromagnetpoles in series and the number of turns of the coils in respectiveelectromagnet poles of the same group are adjusted in such a manner thatthe flux densities of the respective electromagnet poles are graduallychanged along the circumferential direction of the rotary body. Thus,since the flux densities of the respective electromagnet poles aregradually changed in the circumferential direction of the rotary body,the change of the flux densities in the circumferential direction of therotary body becomes small as a whole, and an eddy current is reduced andeddy current loss and rotation loss become small.

In this case, since plural groups of coils are wound around pluralelectromagnet poles, some of the electromagnet poles are wound aroundwith plural groups of the coils.

Moreover, the number of groups of the coils and the number of turns ofthe respective coils of each group in respective electromagnet poles aredetermined in such a manner that the total flux density of respectiveelectromagnet poles becomes the maximum value on the side where therotary body is attracted and the minimum value on the opposite side andthe whole change of the flux density in the circumferential direction ofthe rotary body is, for example, in a cosine wave shape. For example,when the number of electromagnet poles is a multiple of 4, as describedabove, four electromagnets are used as the main electromagnet, theremaining electromagnets are used as a sub-electromagnet, and thecontrol current is determined for the four main electromagnets as usual.

In the case of a homo-polar type magnetic radial bearing, one group ofcoils is provided for each main electromagnet, and an exciting currentcombined with a bias current and a control current is individuallysupplied to the coils of the respective groups. Therefore, four groupsof coils are provided as a whole and four amplifiers are required. Inthis case, the coils of the respective groups are wound around themagnetic poles of the main electromagnet and the sub-electromagnets ofthe group that are on the same side in a direction of control axis ofthe main electromagnet with respect to the center of the rotary body.Also, the number of turns of the coil of respective electromagnet polesis determined so as to change in a cosine wave shape when the mainelectromagnet is regarded as “1”. The control current determined asmentioned above is respectively supplied to the coils of each group.Therefore, the flux densities by the exciting currents in the coils ofeach group are changed in a cosine wave shape when the mainelectromagnet of the group is regarded as “1”. As a whole, the fluxdensities of the respective electromagnet poles become the positivemaximum value on the side where the rotary body is attracted and thenegative minimum value on the opposite side and, moreover, the change ofthe flux densities in the circumferential direction of the rotary bodybecomes a cosine wave shape.

In the case of a hybrid type magnetic radial bearing, one group of coilsis provided for each control axis and a control current is individuallysupplied to the coil of each group. Therefore, two groups of coils areprovided on the whole and two amplifiers are required. In this case, thecoils of each group are wound around the two main electromagnets and allthe sub-electromagnets of the group in the control axis, and the numberof turns of the coil of each electromagnet pole is determined so as tochange in a cosine wave shape when the main electromagnet is regarded as“1”. Moreover, the winding directions of the coils are set to be reversein such a manner that, when the control current is fed in the coils ofeach group, the control magnetic fluxes formed by the coils becomeopposite polarities to each other at the both ends in the direction ofthe control axis with respect to the center of the rotary body.Therefore, when the same control current is fed in the coils of eachgroup, the current on one side in the direction of the control axisbecomes a positive direction and the current on the opposite sidebecomes a negative direction. And the control current determined asmentioned above is supplied to the coils of each group. Accordingly, thecontrol flux densities by the control current in the coils of each groupare changed in a cosine wave shape when the main electromagnet of thegroup is regarded as “1”. The total flux density combined with the biasmagnetic flux and control magnetic flux becomes the maximum value on theside where the rotary body is attracted and the minimum value on theopposite side and the change of the flux density along the wholecircumferential direction of the rotary body becomes a cosine waveshape.

When the number of magnetic poles is a multiple of 3, a three-phaseamplifier which is generally used as a drive amplifier for a motor canbe used for control. For example, in the case of six salient poles, thepresent invention can be realized at low cost by supplying a positive ornegative current to the opposing magnetic poles with a three-phaseinverter. A constitutional example of a magnetic radial bearing in thiscase is shown in FIG. 15. In FIG. 15, the direction x and the directiony of a shaft A are detected by an X-sensor Sx and a Y-sensor Sy. Whenthe shaft A is not in the center, the sensor signals are inputted into acontroller Cont to generate an operational signal for returning theshaft to the center. The operational signals of two phases in the x andy directions are converted into three-phase operational signals of U, V,and W by a 2-phase/3-phase conversion CV and are amplified by athree-phase drive amplifier AP. The control currents of the six salientpoles are controlled by the current.

A controlled type magnetic radial bearing according to the presentinvention is provided with, for example, at least three electromagnetpoles. Each of the electromagnet poles includes a salient pole projectedinside in a radial direction. At both ends of the opposing portion ofrespective salient poles to the rotary body in the whole circumferentialdirection, protruded parts protruding in the circumferential directionare formed so as to be close to each other.

In this case, the number of turns of the coils of each of theelectromagnet poles is set to be the same and the control of controlcurrent in each electromagnet pole can be performed as usual. Further,the flux density is gradually changed in the circumferential directionof the rotary body by forming the protruded parts in a salient pole. Thedifference of the flux densities between a portion having a salient poleand a portion having no salient pole becomes small because the protrudedparts are formed in a close relation together. Therefore, since thechange between the salient poles is reduced, eddy current decreases andan eddy current loss and rotation loss become small.

In addition, as an electromagnet pole according to the presentinvention, so-called closed slot type magnetic poles in which the tipends of each salient pole are connected with adjacent salient poles toeach other by a narrow protruded part can be also adopted. When suchclosed slot type magnetic poles are used, the flux density iscontinuously and smoothly changed in the circumferential direction ofthe rotary body in the salient poles. Therefore, the difference of theflux densities between a salient pole portion and a no salient poleportion becomes very small because the adjacent salient poles areconnected with each other. Since the change between the salient poles isin an extremely smooth state and an eddy current loss and rotation lossare extremely lowered.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a controlled type magnetic radialbearing which shows a first embodiment of the present invention.

FIG. 2 is a longitudinal-sectional view of the first embodiment.

FIG. 3 is a block diagram showing a constitution of a control system ofthe first embodiment.

FIG. 4 is a longitudinal-sectional view of a controlled type magneticradial bearing which shows a second embodiment of the present invention.

FIG. 5 is a block diagram showing a constitution of a control system ofthe second embodiment.

FIG. 6 is a longitudinal-sectional view of a controlled type magneticradial bearing which shows a third embodiment of the present invention.

FIG. 7 is a longitudinal-sectional view of a controlled type magneticradial bearing which shows a fourth embodiment of the present invention.

FIG. 8 is a cross-sectional view of a controlled type magnetic radialbearing which shows a fifth embodiment of the present invention.

FIG. 9 is a block diagram showing a constitution of a control system ofthe fifth embodiment.

FIG. 10 is a cross-sectional view of a controlled type magnetic radialbearing which shows a sixth embodiment of the present invention.

FIG. 11 is a block diagram showing a constitution of a control system ofthe sixth embodiment.

FIG. 12 is a block diagram showing a cross-section of a controlled typemagnetic radial bearing and a constitution of control system, which is aseventh embodiment of the present invention.

FIG. 13 is a block diagram showing a cross-section of a controlled typemagnetic radial bearing and a constitution of a control system, which isan eighth embodiment of the present invention.

FIG. 14 is a cross-sectional view of a controlled type magnetic radialbearing in an embodiment in which closed slot type electromagnet polesare adopted.

FIG. 15 is a block diagram showing an example of constitution of amagnetic radial bearing when control currents in six salient poles arecontrolled by using a three-phase inverter.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereafter, embodiments of the present invention will be described belowwith reference to the drawings.

FIGS. 1 to 3 show a first embodiment. A controlled type magnetic radialbearing of the first embodiment is a homo-polar type, and FIG. 1 is across-sectional view, FIG. 2 is a longitudinal-sectional view and FIG. 3shows a constitution of a control system. In the following description,one of two radial control axes which are perpendicular to each other isset to be an x-axis and the other is set to be a y-axis.

As shown in FIG. 1, a magnetic radial bearing is provided with twelvehomo-polar type electromagnets M1, M2, M3, M4, M5, M6, M7, M8, M9, M10,M11 and M12. Hereafter, these electromagnets are generically shown witha notational symbol “M.” The twelve electromagnets M are arranged withequal intervals in a circumferential direction (called “circumferentialdirection” hereafter) around a rotary body 1, which is disposed, forexample, in a vertical direction. The arranging interval (angle) betweenthe respective electromagnets M is π/6 (=30°), and this is shown as α. Afirst electromagnet M1 is arranged on the positive side of an x-axis(right side in FIG. 1), a seventh electromagnet M7 is arranged on thenegative side of the x-axis (left side in FIG. 1), a fourthelectromagnet M4 is arranged on the positive side of a y-axis (up sidein FIG. 1) and a tenth electromagnet M10 is arranged on the negativeside of the y-axis (under side in FIG. 1) respectively. They are calledmain electromagnets. The remaining electromagnets M2, M3, M5, M6, M8,M9, M11 and M12 are arranged between the main electromagnets M1, M4, M7and M10 at equal intervals. These are called sub-electromagnets.

Rotor parts 2 and 3 using laminated steel plates are respectively formedon an outer peripheral part of the rotary body 1 at two places which areset to have a predetermined interval in an axial direction of the rotarybody 1 (called “axial direction” hereafter), i.e., a vertical directionin FIG. 2. A stator 4 in a circular shape is arranged around the rotorparts 2 and 3 so as to be concentric with the rotary body 1 and theelectromagnets M are provided in the portion of the stator 4.

Especially as shown in FIG. 2, respective electromagnets M are equippedwith a core 5 composed of laminated steel plates whose longitudinalsection is shown in an approximately U-shape and have salient poles 8and 9 composing magnetic poles 6 and 7 which project inside in theradial direction at vertical ends in the axial direction. The uppersalient pole 8 in FIG. 2 is opposed to the upper rotor part 2 in FIG. 2and the lower salient pole 9 is opposed to the lower rotor part 3. Theinner faces (tip end face) of the respective salient poles 8 and 9 inthe radial direction, which are opposed to the outer peripheral faces ofthe rotor parts 2 and 3, are formed in a concave cylindrical face alongthe outer peripheral faces of the rotor parts 2 and 3. Protruded parts 8a and 8 a protruded in the circumferential direction are integrallyformed at both circumferential ends of the tip end face and the tip endparts of the adjacent protruded parts 8 a are arranged so as to be closeto each other in the circumferential direction.

Coils 10 and 11 for feeding an exciting current are respectively woundaround the upper and lower salient poles 8 and 9 of the respectiveelectromagnets M to form magnetic poles 6 and 7. The numbers of turns ofthe coils 10 and 11 of the respective electromagnets M are set to beequal to each other, and the coils 10 and 11 of the upper and lowermagnetic poles 6 and 7 in respective electromagnets M are connected inseries with each other.

Next, with reference to FIG. 3, a control system for the magnetic radialbearing according to the first embodiment will be described. In FIG. 3,only the portions of the rotary body 1 and the magnetic pole 6 of therespective electromagnets M are shown.

Although detailed illustration is omitted, two x-axis-direction positionsensors 12 and 13 for detecting displacement of the rotary body 1 in thex-axis direction and two y-axis-direction position sensors 14 and 15 fordetecting displacement of the rotary body 1 in the y-axis direction areprovided near the electromagnets M.

A controller (control means) 16 for radial direction control whichcontrols the exciting current supplied to the coils 10 and 11 of therespective electromagnets M based on the output signal from the positionsensors 12 to 15 is provided in the magnetic radial bearing. Thecontroller 16 is provided with an x-axis-direction displacementcalculating section 17 for determining a displacement of the rotary body1 in the x-axis direction by calculating the difference between theoutput signals of the two x-axis-direction position sensors 12 and 13,and a y-axis-direction displacement calculating section 18 fordetermining a displacement of the rotary body 1 in the y-axis directionby calculating the difference between the output signals of the twoy-axis-direction position sensors 14 and 15. A PID control section 19 isalso provided for outputting exciting-current signals to the respectiveelectromagnets M based on the displacements of the x-axis direction andthe y-axis direction of the rotary body 1. The exciting-current signalsoutputted to the respective electromagnets M from the PID controlsection 19 are respectively amplified by twelve amplifiers (currentamplifier) A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11 and A12, whichare provided corresponding to the coils 10 of the respectiveelectromagnets M and then supplied. These amplifiers are namedgenerically as a notational symbol A.

As similar to the case of a conventional controlled type magnetic radialbearing having four electromagnets, the PID control section 19 of thecontroller 16 has a function for calculating a control current value Ixcin the x-axis direction with respect to the two main electromagnets M1and M7 in the x-axis direction based on the displacement in the x-axisdirection of the rotary body 1. The PID control section 19 also has afunction for calculating a control current value Iyc in the y-axisdirection with respect to the two main electromagnets M4 and M10 in they-axis direction based on the displacement in the y-axis direction ofthe rotary body 1. These control current values Ixc and Iyc are regardedas a reference control current value.

Next, the PID control section 19 is constituted so as to determine thecontrol current values supplied to the coils 10 of the respectiveelectromagnets M based on the reference control current values Ixc andIyc in such a manner that the control currents in the respectiveelectromagnets M become the maximum value in the positive direction onthe side where the rotary body 1 is magnetically attracted and becomethe minimum value in the negative direction on the opposite side, andare gradually changed in the circumferential direction. These controlcurrent values supplied to the coils 10 of the respective electromagnetsM are generically named as Ic. The PID control section 19 amplifies anexciting-current value signal, which is the sum of a bias-current valuesignal proportional to a constant bias-current value Ic and a controlcurrent value signal proportional to the control current value Iccalculated as described above, and outputs it to the amplifier A. Twelveamplifiers A amplify twelve exciting-current value signals and supplythe excitation signals to the coils 10 of the corresponding twelveelectromagnets M.

The PID control section 19 in this example determines the controlcurrent value Ic supplied to the coil 10 of the respectiveelectromagnets M so that the control current in the respectiveelectromagnets M may be changed in a cosine wave shape. In this case, acontrol current value Ic supplied to an electromagnet M in an arbitraryposition is generally expressed by the following expression. In thefollowing expression, θ is an angle expressing the position of theelectromagnet M, that is, the angle is expressed in the counterclockwisedirection when the position of the first electromagnet M1 (position inthe positive direction of the x-axis) is set to be “0”.Ic=Ixc·|cos θ|+Iyc·|sin θ|(0≦θ≦π/4)  (1)Ic=−Ixc·|cos θ|+Iyc·|sin θ|(π/4≦θ≦π/2)  (2)Ic=−Ixc·|cos θ|−Iyc·|sin θ|(π/2≦θ≦3π/4)  (3)Ic=Ixc·|cos θ|−Iyc·|sin θ|(3π/4≦θ≦π)  (4)

Therefore, when the control current values Ic of the exciting currents(=Io+Ic) supplied to the coils 10 of respective electromagnets M fromthe twelve amplifiers A are respectively Ic1, Ic2, Ic3, Ic4, Ic5, Ic6,Ic7, Ic8, Ic9, Ic10, Ic11 and Ic12, these are expressed as follows:Ic 1=Ixc·cos 0+Iyc·sin 0=Ixc  (5)Ic 2=Ixc·cos α+Iyc·sin α=0.866·Ixc+0.5·Iyc  (6)Ic 3=Ixc·cos 2α+Iyc·sin 2α=0.5·Ixc+0.866·Iyc  (7)Ic 4=Ixc·cos 3α+Iyc·sin 3α=Iyc  (8)Ic 5=−Isc·cos 2α+Iyc·sin 2α=−0.5·Ixc+0.866·Iyc  (9 )Ic 6=−Ixc·cos α+Iyc·sin α=−0.866·Ixc+0.5·Iyc  (10)Ic 7=−Ixc·cos 0+Iyc·sin 0=−Ixc  (11)Ic 8=−Ixc·cos α−Iyc·sin α=−0.866·Ixc−0.5·Iyc  (12)Ic 9=−Ixc·cos 2α−Iyc·sin 2α=−0.5·Ixc−0.866·Iyc  (13)Ic 10=Ixc·cos 3α−Iyc·sin 3α=−Iyc  (14)Ic 11=Ixc·cos 2α−Iyc·sin 2α=0.5·Ixc−0.866·Iyc  (15)Ic 12=Ixc·cos α+Iyc·sin α=0.866·Ixc−0.5·Iyc  (16)

Accordingly, the control currents in the respective electromagnets Mbecome the maximum value in the positive direction on the side where therotary body 1 is attracted and become the minimum value in the negativedirection on the opposite side, and moreover, the change of the controlcurrents becomes a cosine wave shape along the circumferential directionas a whole. Consequently, the exciting current becomes the maximum valueon the side where the rotary body 1 is attracted and becomes the minimumvalue on the opposite side. The exciting currents change in a cosinewave shape between the maximum value and the minimum value, and thechange of the flux density along the whole circumferential directionbecomes a cosine wave shape.

FIGS. 4 and 5 show a second embodiment. A magnetic radial bearingaccording to the second embodiment is of a hybrid type. FIG. 4 shows alongitudinal sectional view and FIG. 5 shows a constitution of a controlsystem. In FIGS. 4 and 5 according to the second embodiment, the samenotational symbol is given to the portion corresponding to the firstembodiment mentioned above in FIGS. 2 and 3.

The magnetic radial bearing is equipped with twelve hybrid-typeelectromagnets m1 to m12 arranged similar to the case of the firstembodiment. As shown in FIG. 4, each of the electromagnets “m” isprovided with a permanent magnet 20 which has magnetic poles at bothvertical ends. A salient pole 8 around which a coil 10 is wound andconstitutes a magnetic pole 6 is arranged at an upper end of thepermanent magnet 20. In addition, a yoke 21 for bias is provided underthe lower end of the permanent magnet 20 in the drawing and the wholeelectromagnet “m” is formed in an approximately U-shape.

The salient pole 8 is constituted of the laminated steel plates andarranged so as to oppose the outer peripheral face of the rotor part 2of the rotary body 1. The yoke 21 is opposed to the outer peripheralface of a flange 22 formed at the lower part of the rotor part 2 of therotary body 1. The permanent magnet 20 is arranged so that all thepolarities on the same upper or lower side in the drawing may become thesame. In this example, the permanent magnet 20 is arranged so that itsupper side is the N pole and the lower side is the S pole. Accordingly,a closed magnetic path is formed by the permanent magnet 20 so as to beformed from the upper end of the permanent magnet 20 to the lower end ofthe permanent magnet 20 through the salient pole 8, the rotary body 1and the yoke 21. An N-pole bias magnetic pole is formed at the end ofthe salient pole 8 and an S-pole bias magnetic pole is formed at the endof the yoke 21. The numbers of turns of the coils 10 of the respectiveelectromagnets “m” are respectively set to be equal.

As shown in FIG. 5, the coils 10 of two electromagnets “m” at theopposing positions in the radial direction are connected in series.Namely, the coils 10 of the first electromagnet ml and the seventhelectromagnet m7, the coils 10 of the second electromagnet m2 and theeighth electromagnet m8, the coils 10 of the third electromagnet m3 andthe ninth electromagnet m9 (not shown), the coils 10 of the fourthelectromagnet m4 and the tenth electromagnet m10 (not shown), the coils10 of the fifth electromagnet m5 and the eleventh electromagnet mill(not shown) and the coils 10 of the sixth electromagnet m6 and thetwelfth electromagnet m12 (not shown) are respectively connected inseries. The same control current is respectively supplied to the coils10 of the two opposing electromagnets “m”, which are connected inseries. In addition, the winding directions of the coils 10 of the twoelectromagnets “m” are reversed in respect to each other in such amanner that, when the same control current is passed in the coils 10 ofthe two opposing electromagnets “m”, the polarities of the magneticfluxes formed by the control current become opposite at the twoelectromagnets “m”. That is, when the same control current is suppliedto the coils 10 of the two opposing electromagnets “m”, one is made inthe positive direction and the other is made in the negative direction.

The constitution of the controller 16 is similar to the first embodimentexcept for the number of amplifiers A and a part of processing in thecontrol section 19. That is, the controller 16 is provided with sixamplifiers A1 to A6, which respectively correspond to the group of thefirst electromagnet m1 and the seventh electromagnet m7, the group ofthe second electromagnet m2 and the eighth electromagnet m8, the groupof the third electromagnet m3 and the ninth electromagnet m9, the groupof the fourth electromagnet m4 and the tenth electromagnet m10 and thegroup of the fifth electromagnet m5 and the eleventh electromagnet m11and the group of the sixth electromagnet m6 and the twelfthelectromagnet m12. In FIG. 5, the connecting relationship about theamplifiers A3 to A6 is omitted, but they are connected in the samemanner as the amplifiers A1 and A2 as described above.

In the controller 16, as in the case of the first embodiment, thecontrol section 19 calculates the reference control current value Ixc inthe X-axis direction and the reference control current value Iyc in theY-axis direction and determines the control current values Ic suppliedto the coils 10 of the respective electromagnets M based on thesereference control current values Ixc and Iye. The control current valuesignals proportional to the control current values Ic are outputted tothe amplifier A. Six amplifiers A amplify the six control current valuesignals and supply the control currents Ic to the coils 10 of the sixcorresponding groups of the electromagnets M.

Also in this example, the control section 19 determines the controlcurrent values Ic supplied to the coils 10 of the six groups of everytwo electromagnets “m” so that the control currents of the respectiveelectromagnets “m” may be changed in a cosine wave shape. In this case,the control current values Ic supplied to an electromagnet which is atan arbitrary position θ are generally expressed as the above-mentionedexpressions (1)˜(4) in the first embodiment. Therefore, when the controlcurrent values Ic supplied to the coils 10 of the six sets of every twoelectromagnets “m” from the six amplifiers A is respectively set to beIc1, Ic2, Ic3, Ic4, Ic5 and Ic6, these will be expressed as theabove-mentioned expressions (5)˜(10) in the first embodiment.Accordingly, the control currents of the expressions (5)˜(10) aresupplied to the coils 10 of the first electromagnet m1 to the sixthelectromagnet m6. In addition, since the winding direction of the coils10 of the seventh electromagnet m7 to the twelfth electromagnet m12 isset to be reversed to that of the coils 10 of the first electromagnet m1to the sixth electromagnet m6, the control currents of theabove-mentioned expressions (11)˜(16) are supplied to the coils 10 ofthe seventh electromagnet m7 to the twelfth electromagnet m12.

By supplying the control currents to the coils 10 of the respectiveelectromagnets “m” as described above, the total magnetic fluxescombined with the bias magnetic flux by the permanent magnet 20 and thecontrol magnetic flux by the control current are formed in the magneticpoles 6 of the respective electromagnets “m”. At this time, the samecontrol current is supplied to the coils 10 of the two electromagnets“m” of each group. However, since one is in the positive direction andthe other is in the negative direction, the polarities of the controlmagnetic fluxes generated on the respective groups of the twoelectromagnets “m” are opposite and the absolute values of the controlflux densities are equal to each other. Also, the polarity of thecontrol magnetic flux is the same as that of the bias magnetic flux,i.e., the N pole, on the side where the rotary body 1 is attracted, andthe polarity of the control magnetic flux is opposite to that of thebias magnetic flux on the opposite side. Therefore, the total fluxdensity becomes larger than the bias flux density on the side where therotary body 1 is attracted and the total flux density becomes smallerthan the bias flux density on the opposite side. The maximum value ofthe control current Ic is set in such a manner that the absolute valueof the control flux density becomes smaller than that of the bias fluxdensity. Therefore, the total magnetic flux combined with the biasmagnetic flux and the control magnetic flux will be the same polarity (Npole) with respect to all the electromagnets M.

Other constitutions and operations are the same as those of the firstembodiment. In the case of the second embodiment, the number of therequired amplifiers A is half the number of the electromagnets “m”.

FIG. 6 shows a third embodiment according to the present invention. Thethird embodiment shows a magnetic radial bearing device in which twosets of upper and lower controlled type magnetic radial bearings 23 and24 are integrally constituted. FIG. 6 shows its longitudinal sectionalview. In FIG. 6 of the third embodiment, the same notational symbols aregiven to the portions corresponding to those of the first embodiment inFIG. 2 and those of the second embodiment in FIG. 4.

The upper magnetic radial bearing 23 is provided with twelveelectromagnets (upper electromagnets) m1 to m12 arranged in a similarmanner as the second embodiment described above. Each of theelectromagnets “m” is equipped with a salient pole 8, around which acoil 10 is wound so as to constitute a magnetic pole 6. Each of thesalient poles 8 is opposed to the outer peripheral face of an upperrotor part 2 of the rotary body 1. The lower magnetic radial bearing 24is equipped with twelve electromagnets (lower electromagnets) m1 to m12arranged in the similar manner as the upper electromagnets “m”. In FIG.6, only two lower electromagnets m1 and m7 are shown. The lowerelectromagnets are shown generically with a notational symbol “m”. Theconstitution of the lower electromagnets “m” is the same as the upperelectromagnets “m” and the same notational symbol is given to the sameportion.

The salient pole 8 of the lower electromagnet “m” is opposed to theouter peripheral face of the lower rotor part 3 of the rotary body 1.Both the outside ends in the radial direction of the salient pole 8 ofthe upper electromagnet “m” and the salient pole 8 of the lowerelectromagnet “m” which are corresponding to each other are connectedwith a permanent magnet 20 in a cylindrical shape. The upper end of thepermanent magnet 20 is formed as an N pole and the lower end is as an Spole as in the case of the second embodiment. Therefore, a closedmagnetic path is formed by the permanent magnet 20, which is from theupper end of the permanent magnet 20 to the lower end of the permanentmagnet 20 via the salient pole 8 of the upper electromagnet “m”, therotary body 1 and then the salient pole 8 of the lower electromagnet“m”. The bias magnetic pole of the N pole is formed in the magnetic pole6 of the upper electromagnet “m” and the bias magnetic pole of the Spole is formed in the magnetic pole 6 of the lower electromagnet “m”.

The constitution of the upper magnetic radial bearing 23 and the lowermagnetic radial bearing 24 is similar to that in the second embodiment.

FIG. 7 shows a fourth embodiment. The fourth embodiment shows a magneticaxial and radial bearing device which is integrally constituted of acontrolled type magnetic axial bearing 25 on an upper side in thedrawing and a controlled type magnetic radial bearing 26 on a lower sidein the drawing. FIG. 7 shows a longitudinal sectional view. In FIG. 7according to the fourth embodiment, the same notational symbol is givento the portion corresponding to that of the second embodiment in FIG. 4described above.

The magnetic axial bearing 25 is equipped with a circular core 28arranged around a flange 27 formed in the rotary body 1. Thelongitudinal-sectional configuration of the core 28 is formed in aU-shape. Ring-shaped magnetic poles 29 and 30 are formed so as tointerpose the flange 27 between both ends of the poles 29 and 30 on theupper and lower sides in the vertical direction. A circular shaped coil31 for feeding a control current for the axial direction is provided onthe outer portion in the radial direction on the inner side of the core28.

The magnetic radial bearing 26 is equipped with twelve electromagnets m1to m12, which are similar to the second embodiment. The outside end inthe radial direction of the salient pole 8 of the respectiveelectromagnets “m” and the outside end in the radial direction of thecore 28 of the axial magnetic bearing 25 are connected with a similarpermanent magnet 20 as that of the second embodiment. A closed magneticpath is formed by the permanent magnet 20, which is from the upper endof the permanent magnet 20 to the lower end of the permanent magnet 20via the upper or lower magnetic pole 29 or 30 of the core 28 of theaxial magnetic bearing 25, the flange 27 of the rotary body 1, therotary body 1, and then the salient pole 8 of the magnetic radialbearing 26 as shown in a solid line in FIG. 7. Accordingly, a biasmagnetic flux is formed between the upper or lower magnetic poles 29 or30 of the axial magnetic bearing 25 and the flange 27, and the magneticflux of an S pole is formed in the salient pole 8 of the magnetic radialbearing 26.

In the axial magnetic bearing 25, a control current is supplied to thecoil 31 from a controller for axial direction control not illustrated.Thereby, as shown in a chain line in FIG. 7, an annular control magneticflux passing through the upper and lower magnetic poles 29 and 30 andthe flange 27 of the rotary body 1 is formed. When the direction of thecontrol current is changed, the direction of the control magnetic fluxalso is changed. The bias magnetic flux is strengthened by the controlmagnetic flux between the flange 27 and one of the magnetic poles 29 and30 and the bias magnetic flux is weakened by the control magnetic fluxbetween the flange 27 and the other of the magnetic poles 29 and 30. Thedirection and magnitude of the control current which are supplied to thecoil 31 are controlled based on a displacement in the axial direction ofthe rotary body 1 that is detected by an axial position sensor notillustrated. Therefore, the rotary body 1 is held at a neutral positionin the axial direction. The constitution of the magnetic radial bearing26 is similar to that of the second embodiment.

FIGS. 8 and 9 show a fifth embodiment according to the presentinvention. A magnetic radial bearing in the fifth embodiment is of ahomo-polar type similar to that of the first embodiment described above.FIG. 8 shows a cross sectional view and FIG. 9 shows a constitution of acontrol system. In FIGS. 8 and 9 in the fifth embodiment, the samenotational symbol is given to the portion corresponding to that of thefirst embodiment in FIGS. 1 and 3.

The magnetic radial bearing is equipped with twelve homo-polar typeelectromagnets M1 to M12 arranged similar to the case of the firstembodiment. The constitution of the respective electromagnets M issimilar to that in the first embodiment shown in FIG. 2 except forwinding of a coil described below.

The magnetic radial bearing is provided with four groups of coils C1,C2, C3 and C4, which are respectively corresponding to the four mainelectromagnets M1, M4, M7 and M10. The coils are generically named asthe notational symbol C. An exciting current combined with a biascurrent and the control current is individually supplied to therespective groups of the coils C from a controller 16. The coil C ofeach group is wound around its main electromagnet M and thesub-electromagnets M that are positioned on the same side in the controlaxis direction as the main electromagnet M with respect to the center ofthe rotary body 1. The number of turns of the coil C of eachelectromagnet M is determined so as to change in a cosine wave shapewhen that of the main electromagnet M is regarded as “1”.

Concretely, a coil (first coil) C1 of a first group is wound around afirst to a third, an eleventh and a twelfth electromagnets M1, M2, M3,M11 and M12. A coil (second coil) of a second group is wound around asecond to sixth electromagnet M2 to M6, a coil (third coil) C3 of athird group is wound around a fifth to a ninth electromagnets M5 to M9and a coil (fourth coil) C4 of a fourth group is wound around an eighthto a twelfth electromagnets M8 to M12.

When the numbers of turns of the first coil C1 and the third coil C3 inthe first electromagnet M1 and the seventh electromagnet M7 are set tobe Nx0 and the numbers of turns of the second coil C2 and the fourthcoil C4 in the fourth electromagnet M4 and the tenth electromagnet M10are set to be Ny0, the number of turns Nx of the first coil C1 or thethird coil C3 wound around an electromagnet at an arbitrary position θand the number of turns Ny of the second coil C2 or the fourth coil C4are generally expressed as the following expressions.Nx=Nx 0·|cos θ|  (17)Ny=Ny 0·|sin θ|  (18)

Accordingly, when the numbers of turns of the first coil C1 or the thirdcoil C3 in the respective electromagnets M are set to be Nx1 to Nx12 andthe numbers of turns of the second coil C2 or the fourth coil C4 are setto be Ny1 to Ny12, these are expressed as follows.Nx 1=Nx 7=Nx 0·cos 0=Nx 0  (19)Nx 2=Nx 6=Nx 8=Nx 12=Nx 0·cos θ=0.866·Nx 0  (20)Nx 3=Nx 5=Nx 9=Nx 11=Nx 0·cos 2θ=0.5·Nx 0  (21)Nx 4=Nx 10=Nx 0·cos 3θ=0  (22)Ny 1=Ny 7=Nx 0·sin 0=0  (23)Ny 2=Ny 6=Ny 8=Ny 12=Ny 0·sin α=0.5·Ny 0  (24)Ny 3=Ny 5=Ny 9=Ny 11=Ny 0·sin 2α=0.866·Ny 0  (25)Ny 4=Ny 10=Ny 0·sin 3α=Ny 0  (26)

Normally, Nx0 and Ny0 are equal.

The constitution of the controller 16 is similar to the first embodimentexcept for the number of amplifiers A and a part of processing in acontrol section 19. The controller 16 is provided with four amplifiersA1, A2, A3 and A4 respectively corresponding to four groups of the coilsC.

In the controller 16, as the first embodiment, the control section 19calculates a control current value Ixc in an X-axis direction and acontrol current value Iyc in a Y-axis direction and outputs a signalcombined with a bias-current value signal proportional to a constantbias-current value Io and a control current value signal proportional tothe control current values Ixc and Iyc to the corresponding amplifier Aas an exciting-current value signal. Four amplifiers A amplify fourexciting-current value signals and supply exciting currents to fourcorresponding coils C. When the exciting-current value supplied to thefirst coil C1 from the first amplifier A1 is I1, the exciting-currentvalue supplied to the second coil C2 from the second amplifier A2 is I2,the exciting-current value supplied to the third coil C3 from the thirdamplifier A3 is I3 and the exciting-current value supplied to the fourthcoil C4 from the fourth amplifier A4 is I4, these are expressed asfollows.I 1=I 0+Ixc  (27)I 2=I 0+Iyc  (28)I 3=I 0−Ixc  (29)I 4=I 0−Iyc  (30)

In this case, the same exciting current is supplied to the coils C ofthe respective groups. As mentioned above, since the numbers of turns ofthe coils C of each group are changed based on the position of theelectromagnets M, the flux densities by the exciting current in thecoils C of each group are changed in a cosine wave shape when the mainelectromagnet M of the group is regarded as “1”. As a whole, the fluxdensities by the respective electromagnets M become the positive maximumvalue on the side where the rotary body 1 is attracted and become thenegative minimum value on the opposite side and, moreover, the change ofthe flux density in the circumferential direction becomes in a cosinewave shape.

FIGS. 10 and 11 show a sixth embodiment according to the presentinvention. A magnetic radial bearing of the sixth embodiment is a hybridtype similar to the second embodiment and has a constitution similar tothe fifth embodiment. FIG. 10 shows a cross sectional view and FIG. 11shows a constitution of a control system. In FIGS. 10 and 11 in thesixth embodiment, the same notational symbol is given to the portioncorresponding to the fifth embodiment described above in FIGS. 8 and 9.

A magnetic radial bearing is equipped with twelve hybrid typeelectromagnets M1 to M12 arranged in a similar manner as the secondembodiment. The constitution of each electromagnet M is similar to thesecond embodiment shown in FIG. 4 except for winding of the coil asdescribed below.

The magnetic radial bearing in the present embodiment is provided withtwo groups of coils C1 and C2 corresponding to an X-axis and a Y-axisrespectively. Control currents are individually supplied to the coils Cof respective groups from the controller 16. The coil C of each group iswound around two main electromagnets M of the control axis of the groupand all the sub-electromagnets M. The numbers of turns of the coil C ofeach electromagnet M are determined so as to be changed in a cosine waveshape when the main electromagnet M is regarded as “1”.

Concretely, the coil (first coil) C of the first group is wound around afirst to a third electromagnets M1 to M3, a fifth to a ninthelectromagnets M5 to M9 and an eleventh and a twelfth electromagnets M11and M12. The coil (second coil) C2 of the second group is wound around asecond to a sixth electromagnets M2 to M6 and a seventh to a twelfthelectromagnets M7 to M12.

When the number of turns of the first coil C1 in the first electromagnetM1 and the seventh electromagnet M7 is set to be Nx0 and the number ofturns of the second coil C2 in the fourth electromagnet M4 and the tenthelectromagnet M10 is set to be Ny0, the number of turns Nx of the firstcoil C1 and the number of turns Ny of the second coil C2 wound aroundthe electromagnet at an arbitrary position θ are generally expressed bythe aforementioned expressions (17) and (18).

Therefore, when the numbers of turns of the first coil C1 in therespective electromagnets M are set to be Nx1 to Nx12 and the numbers ofturns of the second coil C2 are set to be Ny1 to Ny12, these areexpressed by the aforementioned expressions (19) to (26).

The first coil C1 is wound around five pairs of electromagnets M whichare opposed to each other in the radial direction. The windingdirections of the coil C1 of the opposing two electromagnets M arereversed to each other so that one of the opposing electromagnets M isin the positive direction and the other is in the negative directionwhen a control current is supplied in a manner described later.

A constitution of the controller 16 is similar to the fifth embodimentexcept for the number of amplifiers A and a part of processing in thecontrol section 19. The controller 16 is provided with two amplifiers A1and A2 corresponding respectively to two groups of coils C.

In the controller 16, as similar to the second embodiment, a controlsection 19 calculates a control current value Ixc in an X-axis directionand a control current value Iyc in a Y-axis direction and outputscontrol current value signals proportional to these control currentvalues Ixc and Iyc to the corresponding amplifiers A. The controlcurrent Ixc is supplied to the first coil C1 from the first amplifier A1and the control current Iyc is supplied to the second coil C2 from thesecond amplifier A2. Thereby the control current Ixc is supplied to thefirst coil 1 of the first to the third electromagnets M1 to M3, theeleventh and the twelfth electromagnets M11 and M12. On the other hand,the control current (−Ixc) in the opposite direction is supplied to thefifth to the ninth electromagnets M5 to M9 since the winding directionof the first coil C1 is reversed as described above. Similarly, thecontrol current Iyc is supplied to the second coil C2 of the second tothe sixth electromagnets M2 to M6. On the other hand, the controlcurrent (−Iyc) in the opposite direction is supplied to the eighth tothe twelfth electromagnets M8 to M12 since the winding direction of thesecond coil C2 is reversed as described above.

In this case, the same exciting current is respectively supplied to thecoils C of the respective groups. However, as described above, since thenumbers of turns of the coils C of each group are changed dependent onthe positions of the electromagnets M, the flux densities by the controlcurrent in the coils C of each group are changed to a cosine wave shapewhen the two main electromagnets M of the group are regarded as “1”.That is, the total flux density combined with the bias magnetic flux andthe control magnetic flux becomes the positive maximum value on the sidewhere the rotary body 1 is attracted and the negative minimum value onthe opposite side and, moreover, the change of the flux density in thecircumferential direction is formed in a cosine wave shape.

In the magnetic radial bearings of the above-mentioned first to thesixth embodiments, protruded parts 8 a are formed in the portion of therespective salient poles 8 and 9 of each electromagnet M, which areopposed to the rotor parts 2 and 3 of the rotary body 1. Accordingly,the flux density is gradually changed also in the portion of the salientpoles 8 and 9 in the circumferential direction. Since the adjacentprotruded parts 8 a of the salient poles 8 and 9 are closely positionedto each other, the difference of the flux densities between a portionwith the salient poles 8 and 9 and a portion having no salient poles 8and 9 becomes small and the change of the flux density between thesalient poles 8 and 9 becomes small. Consequently, the change of theflux density in the circumferential direction becomes smaller as awhole. However, such protruded parts 8 a of the salient poles 8 and 9are not necessarily required in magnetic radial bearings of theconstitution such as the first to the sixth embodiments.

FIG. 12 shows a seventh embodiment according to the present invention. Amagnetic radial bearing of the seventh embodiment is of a homo-polartype and FIG. 12 shows a cross sectional view and a constitution of acontrol system. In FIG. 12 according to the seventh embodiment, the samenotational symbol is given to the portion corresponding to the firstembodiment in FIGS. 1 and 3.

The magnetic radial bearing is equipped with four homo-polar typeelectromagnets M1, M2, M3, and M4 disposed with equal intervals in thecircumferential direction in a similar manner as a conventionalhomo-polar type magnetic radial bearing. These four electromagnets M1,M2, M3 and M4 are respectively correspond to the four mainelectromagnets M1, M4, M7 and M10 in the first embodiment.

The constitution of each electromagnet M is similar to that of the firstembodiment shown in FIG. 2. An inner face (end surface) in the radialdirection of the respective salient poles 8 and 9 opposing to the rotorparts 2 and 3 is formed in a concave circular shape along the outerperipheral face of the rotor parts 2 and 3. Protruded parts 8 a and 8 aprojected in the circumferential direction are integrally formed at bothends of the end surface in the circumferential direction and theadjacent protruded parts 8 a in the circumferential direction is closelypositioned to each other. Moreover, coils 10 to which an excitingcurrent is individually supplied are respectively wound around thesalient poles 8 of the electromagnets M.

The constitution of a controller 16 is similar to that of the fifthembodiment shown in FIG. 9. Exciting currents I1, I2, I3 and I4expressed by the aforementioned expressions 27 to 30 are supplied to thecoils 10 of the respective electromagnets M from the controller 16.Other constitution is similar to that of the first or the fifthembodiment.

FIG. 13 shows an eighth embodiment according to the present invention. Amagnetic radial bearing of the eighth embodiment is of a hybrid type andsimilar to the constitution of the seventh embodiment. FIG. 13 shows across sectional view and a constitution of a control system. In FIG. 13according to the eighth embodiment, the same notational symbol is givento the portion corresponding to the first embodiment in FIGS. 3 and 5and the seventh embodiment in FIG. 12.

The magnetic radial bearing is equipped with four hybrid typeelectromagnets M1 to M4 arranged in a similar manner as the seventhembodiment. The constitution of each electromagnet M is similar to thatof the second embodiment shown in FIG. 4. Coils 10 of two electromagnetsM1 and M3 in an X-axis direction are connected in series and the samecontrol current is supplied to the coils 10. Also, the windingdirections of the coils 10 of the respective electromagnets M1 and M3are reversed to each other in such a manner that one of the coils is inthe positive direction and the other is in the opposite direction whenthe same control current is supplied to the coils 10 of the twoelectromagnets M1 and M3, The constitution of two electromagnets M2 andM4 in a Y-axis direction is similar to that of the two electromagnets M1and M3

The constitution of a controller 16 is similar to that of the sixthembodiment shown in FIG. 11. The control current Ixc is supplied to thecoils 10 of the two electromagnets M1 and M3 in the X-axis directionfrom the controller 16 and the control current Iyc is supplied to thetwo electromagnets M2 and M4 in the Y-axis direction.

Other constitutions are similar to those of the second, sixth andseventh embodiments, but the electromagnets such as those as shown inFIG. 6 or 7 can also be applied to the electromagnet in the eighthembodiment.

In the magnetic radial bearing according to the seventh and eighthembodiments described above, the protruded parts 8 a are formed in theportion of the salient poles 8 and 9 of each electromagnet M opposing tothe rotor parts 2 and 3 of the rotary body 1. Accordingly, the fluxdensity is gradually changed in the portion of the salient poles 8 and 9along the circumferential direction. Also, since the adjacent protrudedparts 8 a of the salient poles 8 and 9 are closely positioned to eachother, the difference of the flux densities between the portion withsalient poles 8 and 9 and the portion with no salient poles 8 and 9becomes small, and thus the change of the flux density between salientpoles 8 and 9 becomes small. Consequently, the change of the fluxdensity along the circumferential direction becomes smaller as a whole.

In an embodiment shown in FIG. 14, so-called closed slot typeelectromagnet poles are used for a magnetic radial bearing. The magneticradial bearing is provided with twelve homo-polar type electromagnetsM1, M2, M3, M4, M5, M6, M7, M8, M9, M10, M11 and M12, similar to thefirst embodiment described above. A salient pole 8 is formed so as toproject inside in the radial direction in each of the electromagnets Mand protruded parts 8 a and 8 a protruded in the circumferentialdirection are integrally formed at both ends of the inner face (endsurface) in the radial direction of the salient pole 8 of theelectromagnets M along the circumferential direction. Thecircumferential end portions of the adjacent protruded parts 8 a areconnected with each other.

When such closed slot type electromagnet poles are used, the fluxdensity is changed continuously and extremely smoothly in the portion ofthe salient pole 8 along the circumferential direction of the rotarybody. Accordingly, the difference of the flux densities between theportion with salient pole and the portion with no salient pole almostdisappears by the connection of the adjacent salient poles 8 and 8 andthe flux densities between the salient poles 8 are changed in anextremely smooth state. Therefore the eddy current loss and rotationloss are reduced.

INDUSTRIAL APPLICABILITY

The controlled type magnetic radial bearing according to the presentinvention is useful for an energy-storage flywheel, an ultra high-speedrotating body or the like which is supported in a non-contact manner ina radial direction.

1. A controlled type magnetic radial bearing provided with pluralelectromagnet poles having a core wound around with a coil and arrangedat predetermined intervals along a circumferential direction of a rotarybody at the same position in an axial direction of the rotary body, allof the electromagnet poles being set in the same polarity, characterizedin that the flux densities in the electromagnet poles are graduallychanged in the circumferential direction of the rotary body.
 2. Thecontrolled type magnetic radial bearing according to claim 1, whereinthe number of the electromagnet poles is at least three.
 3. Thecontrolled type magnetic radial bearing according to claim 2, whereinthe flux densities of the respective electromagnet poles are graduallychanged along the circumferential direction of the rotary body byadjusting a control current supplied to the coil wound around each ofthe electromagnet poles.
 4. The controlled type magnetic radial bearingaccording to claim 2, wherein each of the electromagnet poles isprovided with plural groups of coils to which a control current isindividually supplied and the flux densities of the respectiveelectromagnet poles are gradually changed along the circumferentialdirection of the rotary body by means of winding the coils of each grouparound plural predetermined electromagnet poles in series and adjustingthe number of turns of each coil of the same group with respect to eachof the electromagnet poles.
 5. The controlled type magnetic radialbearing according to claim 4, wherein the electromagnet poles arearranged in such a manner that sub-electromagnets are positioned on bothsides of a main electromagnet and the number of turns of coil of eachelectromagnet is determined so as to change in a cosine wave shape whenthat of the main electromagnet is regarded as “1”.
 6. The controlledtype magnetic radial bearing according to claim 5, wherein the number ofturns of coil of the sub-electromagnet is set to be N0·|cos θ|, where θis a position of the sub-electromagnet with respect to the mainelectromagnet at the starting point and N0 is the number of turns ofcoil of the main electromagnet.
 7. The controlled type magnetic radialbearing according to claim 6, wherein, when the numbers of turns of coilin the x-axis and the y-axis directions of the main electromagnet areset to be Nx0 and Ny0, the number of turns Nx and the number of turns Nywound around the sub-electromagnet at an arbitrary position θ areexpressed as the following expressionsNx=Nx 0·|cos θ|Ny=Ny 0·|sin θ|.
 8. The controlled type magnetic radial bearingaccording to claim 5, wherein the electromagnet poles are arranged insuch a manner that combinations of the main electromagnet and thesub-electromagnets positioned on both sides of the main electromagnetare disposed on both sides with respect to the rotary body and the coilsof each group are connected in series with each other and wound aroundin opposite directions.
 9. The controlled type magnetic radial bearingaccording to claim 2, wherein the electromagnet poles are provided withsalient poles projected in the radial direction, both ends of theportion of each salient poles that are opposed to the rotary body areformed with protruded parts protruded in the circumferential directionof the rotary body, and the protruded parts of the adjacent salientpoles are formed so as to be close each other.
 10. The controlled typemagnetic radial bearing according to claim 2, wherein the electromagnetpoles are provided with salient poles projected in the radial direction,both ends of the portion of each salient poles that are opposed to therotary body are formed with protruded parts protruded in thecircumferential direction of the rotary body, and the magnetic flux iscontinuously changed in the circumferential direction of the rotary bodyby means of that the protruded parts of the adjacent salient poles areconnected with each other.
 11. The controlled type magnetic radialbearing according to claim 1, wherein the number of the electromagnetpoles is a multiple of three or four.
 12. The controlled type magneticradial bearing according to claim 1, wherein the electromagnet isprovided with a permanent magnet which has magnetic poles in the axialdirection to form bias magnetic poles.